1. Field of the Invention
The present invention relates to a ring detector and a method therefor, and more particularly, to a circuit and a method for detecting a ring in a wireless/wired composite telephone system.
2. Description of the Related Art
The operation of a circuit for detecting a ring in an earlier wireless/wired composite telephone system will be described with reference to FIGS. 1 and 2.
If no ring is received, a voltage difference of a direct current (DC) component ("V.sub.A ") of 45-75 volts occurs at both tip and ring terminals. However, if a ring is received, an alternating current (AC) component having a frequency of 18-60 Hz is superimposed on the DC component V.sub.A of 45-75 V to then be supplied to a telephone. The signal supplied to the telephone has such a format as shown in FIG. 2A.
The supplied signal has its the DC component V.sub.A removed by a DC blocking circuit 110 and outputs a signal having a frequency of 18-60 Hz ("V.sub.B "). The V.sub.B signal is shown in FIG. 2B and is supplied to a ring detector 112. The ring detector 112 outputs a signal shown in FIG. 2D ("V.sub.D ") if the V.sub.B signal corresponds to the specifications. The V.sub.D signal shown in FIG. 2D is an audible signal having a frequency of 600-1200 Hz and notifies ring reception by oscillating a buzzer 114 of a wired telephone.
An attenuator 116 includes zener diodes D1 and D2 for adjusting voltages to output the V.sub.B signal applied from the DC blocking circuit 110 as the signal limited to a Zener breakdown voltage level. The signal limited to a Zener breakdown voltage level is supplied to an optical coupler 118 to supply a signal having a format shown in FIG. 2C ("V.sub.C ") to a CPU 120. Accordingly, the CPU 120 controls the wireless telephone to notify ring reception.
Now, a ring detection method will be described with reference to FIGS. 1 and 3.
In step 310, it is determined whether an inverting signal corresponding to an interrupt by ring reception is detected by an interrupt port of the CPU 120. If the inverting signal is detected, the process proceeds to a step 312 and measures the frequency of a signal supplied to the optical coupler 118 to determine whether the measured frequency corresponds to a ring frequency. If it is determined in the step 312 that the measured frequency is a ring frequency, the CPU 120 detects a ring on time of the supplied signal in step 314. Whenever the ring on time is detected, the CPU 120 calls up the wireless telephone to notify ring reception in step 316. In response thereto, the calling for notifying ring reception is continuously performed until a hook-off is detected in step 318.
In this earlier wireless/wired composite telephone system, since a ring-dedicated chip is used for the ring detector of a wired telephone, there is no induced problem.
However, since the ring detector of a wireless telephone requires an attenuator for attenuating a ring signal and limiting the same, it is difficult to simplify the circuit. Further, due to increased raw material cost and cumbersome operational processes, the manufacturing cost becomes increased.
Another problem of the ring detector is in that a general input/output port cannot be used but only an interrupt port can be used. Also, in order to measure the frequency, the memory size must increase depending on the increased software.